1. Field of the Invention
The present invention relates to an antenna switching device for switching three or more antennas, and in particular, to the device, the method, and the storage medium, whereby a diversity antenna can be switched.
2. Description of the Related Art
Terrestrial radio communications are influenced of multi pass propagation for reflection by the building or other objects. If the phases of radio waves arriving from different propagation paths coincide in the same phase, then the electric field becomes stronger, and if they are in opposite phase, then the electric field becomes weaker. A communications device in a moving object moves through an electric field which varies in this way, and it is affected fading. In order to reduce fading effects, a diversity antenna switching method has been proposed.
A diversity antenna switching method utilizes the fact that if two or more antennas are provided and if the frequency, or the polarization, or the directivity, or the positions, are different between the antennas, then the received field strength will be different in the antennas, in which case, the antenna having the stronger received level is selected for receiving, thereby reducing fading effects.
It is relatively easy to switch between two antennas, and devices (integrated circuits: IC) for this purpose are commercially available. However, if using diversity involving three or more antennas, this processing is relatively complex. For example, the levels received by the antennas are accumulated and are all compared with each other in order to select the optimum antenna.
Desirably, it would be possible to select an optimum antenna from three or more antennas, by appending a simple circuit to an existing device (IC) which is only capable of switching between two antennas. Moreover, desirably, it would also be possible to apply this system to any type of diversity antenna.